Part Number: UCC28070
I am using UCC28070 interleaved PFC controller for 1.2kW battery charger design. I have few queries regarding this IC. These are mentioned below.
1. Does duty cycle in boost PFC varies according to input sine voltage?
2. What are the advantages and disadvantages if we keep duty cycle constant?
3. What are the advantages and disadvantages if we keep duty cycle variable?
4. Why loop bandwidth of PFC is always kept low such as at 20Hz?
In reply to John Griffin1:
Hello John, Thanks for reply. Can you please let us know the use of the boost bypass diode as highlighted in attached image. Our input ac rms voltage range is 165 to 295 and o/p of PFC is 420V . So please let us know the use case of boos bypass diode in our application? Regards, Dhananjay Yadav
In reply to Dhananjay Yadav:
Hello, 1. Below screenshot is from datasheet of UCC28070 (Page no: 32). Please see highlighted box in red color. Can you please let us know why output capacitor is considered at twice the line frequency?
2. Is Protection from undervoltage and overvoltage on AC input line is available on UCC28070? Regards, Dhananjay
Hello, 1. Regarding low AC input voltage: It is understood that Vout will decrease as 28070 will go into current limit and duty cycle limit also reaches. But I could not find the value in datasheet at VSENSE pin where UCC28070 turns off. Please guide. 2. If Under voltage protection is already present, then why it is added externally in TI's one of the reference design? Please refer to below image.(File: PMP4311A_Sch_RevA.sch) 3. As there is no protection from over voltage , so we need to add external circuitry for this right? 4. But in case of overvoltage, where VINAC peak value > VPFC output, 28070 will reduce duty cycle(28070 will go into voltage limit cycle) and at certain AC input over voltage it will become zero right? Regards, Dhananjay Yadav
Hello John, Thanks. We have another query. In ZVT section, a resistor and capacitor is placed in series with gate drive transformer primary coil winding. Can you please let me know the reason behind this? And how to select these resistor capacitor values. When we are simulating below circuit, the waveform is settling after 300usec approx. Considerinf 200KHz switching frequency, will there be a problem? Please guide in selecting cap and resistor value. Regards, Dhananjay Yadav
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